Cmd, regedit and task manager are being used by another program

I cant use my task manager. regedit or cmd, i've tried various ways to fix the problem, with no luck, i've also ran ad-aware, malwarebytes, mcafee virus scans, and removed whaterver was found, my pc is also running quite slow, and i only just re-installed windows, i need urgent help, as i canot complete my work, among other things and it is completely anoying, help would be much appreciated, thanks.